A. Field of the Invention
The invention relates generally to an apparatus and method, for the application of a solvent reactive, heat-shrink film or label, to a container having a curvilinear, frusto-conical or other irregular aspect to the configuration of its outer wall. More specifically, the invention contemplates applying adhesive and solvent upon selective areas of a label, wrap applying a portion of the label completely around the container so that the overlapped ends form a strong seam, and then heating the label to conform the remaining portion to the curved, conical, or irregular section of the container.
It is well recognized that in certain applications, heat shrink labels provide a number of distinct advantages over paper and non-shrinkable plastic labels. For example, if the label or film is to be applied to a container or article having a curved, conical, or irregular surface underlying the label, the heat-shrink label can readily be shrunk to conform to the surface anomalies of the container. This conforming capability, in turn, provides an aesthetically pleasing appearance for the labeled container. And, in applications where the shrunken label extends around the bottom of the container, the label forms a sturdy base and insulates the heated or cooled contents from direct contact with the user's hand. However, the application of heat shrunk labels to such containers poses special problems not typically encountered in a more conventional setting, where the labels are non-shrinkable in nature, and the only aspect of the containers to be labeled is right-circular cylindrical, and straight-walled in configuration.
Solvent has proven an effective bonding agent for full wrap plastic or polymer labels, providing the mating ends of the label are brought into positive, and preferably compressive contact, quickly after application of solvent to the overlapping trailing end. Nevertheless, if the solvent is allowed to dry, even partially, before coming into compressive contact with the mating surface, a poor bond will form and the label ends will likely separate. This phenomenon is generally not a problem when labeling right-circular cylindrical containers, particularly where the only surface to be labeled is of uniform configuration. In this labeling application, the label is only intended to cover the right-circular cylindrical portions of the container, as opposed to any curved, conical, or irregular portions. In the former instance, the full extent of the label seam or overlapping ends is supported by the container wall at the initial moment of label end overlap. Consequently, the container wall provides a convenient backing support against which a rolling compressive force can be applied to effect a strong bond between the overlapping ends.
This rolling compressive force may be applied by a rotary, label transport vacuum drum cooperating with a curved, concentric, stationary roll-on pad, spaced approximately a container's diameter away from the periphery of the drum. The vacuum drum applies the label to the container and the roll-on pad causes the container to rotate and compressively wrap-apply the label thereto. Other apparatus, such as a linear, driven roll-on belt, or the like, working in conjunction with an opposing linear roll-on pad can be employed as well. Providing the label seam is supported and compressed during the initial bonding period, the solvent forms a very strong seal between the overlapping label ends.
A different situation is presented when a section of the label extends beyond the supportive wall of the container. This may occur when the label, prior to being heat shrunk, extends beyond the upper or lower end of the container, or where the container surface itself presents curves or discontinuities. In these applications, which appropriately call for the use of heat shrink label material, there is no backing or support for at least a section or portion of the label seam, against which the rolling compressive forces can be applied. As a consequence, when solvent is used as an agent to bond the overlapping trailing and leading ends of the label, inconsistent and faulty bonding may occur in this unsupported region of the label seam. And the larger the extent of the unsupported seam, the greater the likelihood that faulty bonding will occur.
The use of solvent to bond the ends of heat shrink labels is particularly difficult in the above-mentioned applications, since these labels tend to be particularly thin and flimsy in nature. Without the application of compressive forces against the label seam at the critical moment of initial end overlap, the limp label has a tendency to flex, sag, or buckle, all of which will lessen the chances of a good bond forming. Without a good bond between the overlapped ends, the subsequent application of heat and attendant stretching forces can easily cause label end separation, uneven shrinking, or an unsightly label seam.
B. Description of the Prior Art
The use of hot-melt adhesives and solvent reactive adhesives in a roll-fed labeling machine, is discussed in King, U.S. Pat. No. 4,544,431. Fosnaught, U.S. Pat. No. 4,574,020 teaches the gravure roll application of solvent upon both the leading and trailing ends of a label, before the label is wrapped around a container. U.S. Pat. No. 4,406,721, issued to Hoffmann, discloses the application of a heat shrinkable film to a container, whereafter heat is applied to free-standing portions of the label to shrink them onto the container. U.S. Pat. No. 4,735,668, granted to Hoffmann, teaches a method of applying a plastic label segment to a container, wherein hot melt adhesive is applied to the label's leading edge and solvent is applied to the label's trailing edge.
The applicant herein, in U.S. application Ser. No. 07/202,610 illustrates the use of ejection-applied hot melt adhesive and wipe-applied solvent, respectively, upon leading and trailing end portions of a label, before wrapping that label around a container.